Solenoid magnet

ABSTRACT

The armature of an electromagnet moves axially in two coaxial, annular pole pieces axially separated by the coil of the magnet when the coil is energized. In another electromagnet, radially projecting pole pieces of a rotor may be aligned simultaneously with corresponding pole pieces equiangularly spaced on the stator against the restraint of a return spring when the stator pole pieces are excited by an energized coil.

United States Patent 1191 Ueno et al. Sept. 24, 1974 SOLENOID MAGNET2,575,153 11/1951 Wightman 310/261 x 3,119,940 1/1964 Pettit et al. [75]Inventors Km'akawar 3,221,191 11/1965 Cuches et al. 335/279 x both ofTokyo, Japan [73] Assignee: Kabushiki Kaisha Akuto Giken,

Tokyo, Japan Primary ExaminerG. Harris [22] Filed: g 30 1973 Attorney,Agent, or F1rmHans Berman [21] Appl. No.: 393,041

30 Foreign Application Priority Data 1571 ABSTRACT Sept. 2, 1972 Japan47-88147 The armature of an electromagnet moves axially in [52] US. Cl335/255, 335/272, 310/259, two x nn r pole pie es axially separated by310/269 the coil of the magnet when the coil is energized. In [51] Int.Cl. H01t 7/08 another electromagnetr radially p j g po e p e es [58]Field of Search 335/255, 272, 279; of a rotor may be alignedSimultaneously with corre- 310/254, 258, 262, 269, 259, 261 spondingpole pieces equiangularly spaced on the stator against the restraint ofa return spring when the [56] References Cited stator pole pieces areexcited by an energized coil.

UNITED STATES PATENTS 2,560,560 7/1951 Doherty 310/259 10 Claims, 15Drawing Figures PAIEMEB EPMM memo SHEEF 1 My I? /4d 14 Megneficaifracfive force Magnefic affraciive force SOLENOID MAGNET Thisinvention relates to electromagnetic driving apparatus, and particularlyto apparatus in which a force of attraction is exerted on an armaturewhen a core is excited by current flowing in a coil.

In conventional electromagnetic devices in which an armature moveslinearily toward and away from a core, the force of attraction issmallest initially when the ar mature is farthest from the core andgreatest when the armature is nearest the core at the end of itsmovement. If the attracted armature abuttingly engages the core, damageto both elements may occur in continued use.

In known devices, in which the armature rotates within an envelopingstator toward a position in which radially projecting pole pieces of thestator and rotor are aligned, the initial force of attraction exerted onthe armature is not as weak as in the first-described device, butgreater initial torque than is available in the known devices would bedesirable.

It is an important object of this invention to provide electromagneticdriving apparatus of the general type described in which the drivingcomponent of the magnetic force of attraction is high initially anddecreases almost to zero as the armature reaches the end of its stroke.

Other features, objects, and advantages of this invention will appearmore fully from the following description when considered in connectionwith the appended drawing in which:

FIG. 1(A) shows a known electromagnet arrangement in section;

FIG. 1(B) graphically illustrates the relationship between the lineardisplacement of the armature and the driving magnetic force exerted onthe same in the apparatus of FIG. 1(A);

FIG. 2 shows an electromagnet arrangement of the invention in sideelevation and partly in section;

FIG. 3 is a fragmentary view of another electromagnet arrangementaccording to the invention;

FIG. 4 shows the relationship of armature displacement and magnetic focein the apparatus of FIG. 3 and FIG. 9 in the manner of FIG. 1(8);

FIG. 5(A) illustrates the stator frame of a rotary magnet arrangement ofthe invention in section on its axis;

FIG. 5(B) shows the device of FIG. 5(A) in section on the line 5-5;

FIG. 5(C) shows the stator frame of FIG. 5(A) assembled with theassociated rotor and exciting coil in a corresponding view;

FIG. 6(A) illustrates the rotor of the apparatus of FIG. 5(C);

FIG. 6(B) shows the same rotor in a view corresponding to FIG. 5(B);

FIG. 7(A) shows the coil of the apparatus of FIG. 5(C) partly inelevation and partly in axial section;

FIG. 7(B) is aplan view of the coil of FIG. 7(A);

FIG. 8 shows a modified stator and the associated rotor in a viewcorresponding to that of FIG. 5(C);

FIG. 9 is a perspective view of a modified rotor; and

FIG. 10 is a perspective, exploded view of the apparatus of FIG. 5(C).

The known magnet arrangement shown in FIG. l(A) has a rod-shapedarmature l0 coaxially movable in a cylindrical coil 12. The coil isenveloped by a unitary, cup-shaped frame 14 of magnetic material. Whenthe coil 12 is energized, a cylindrical wall portion 14a and a radialend wall of the frame 14 provide a yoke connecting an annular flange 14bconstituting one pole piece of the electromagnet and another pole pieceMe which projects centrally from the end wall 140 and is formed with arecess 14d shaped to receive one end of the armature rod III.

The attracted armature I0 strikes the pole piece Me.

As is shown in FIG. 1(8), the force of attraction acting in thedirection of movement on the armature 10 in the initial position of FIG.1(A) is at its minimum value and increases until the armature strikesthe pole piece l4e. During extended use of the known device, theengagement faces of the armature l0 and of the pole piece l4e are wornand deformed. They may become heated sufficiently to make the deviceinoperative.

The improved electromagnet arrangement of the invention shown in FIG. 2avoids this shortcoming.

The frame of the arrangement is formed by a cylindrical, tubular casing20 of magnetizable material. Brackets 22, 24 of non-magnetic materialproject radially inward from the axial ends of the casing 20. Twoaxially spaced, annular pole pieces 26, 28 are coaxially fastened to theinner face of the casing 20.

A coil 32 is wound on a cylindrical carrier tube 30 of non-magneticmaterial between radial flanges 30a, 30b. The inner diameter of the tube30 is slightly smaller than the corresponding dimension of the polepieces 26, 28 which are separated by the coil 32 and the tube 30. Anarmature 34 passes coaxially through the casing 20, through centralapertures in the pole pieces 26, 28 and in the coil 32. It is mounted onnon-illustrated bearings for axial movement. It consists of a rod 36carrying two annular bodies 38, 40 of magnetizable material arranged anddimensioned to be received simultaneously in the central openings of thepole pieces 26, 28 when the coil 32 is energized, as shown in FIG. 2.Only the portion of the rod 36 between the annular bodies 38, 40consists of or is coated with magnetizable material. A helicalcompression spring 42 wound about the rod 36 between the body 40 and thebracket 24 returns the armature to the rest position partly indicated inbroken lines when the coil 12 is deenergized.

The magnetic force of attraction axially exerted on the armature 34 isat its maximum in the rest postion and decreases as the armatureapproaches the position shown in FIG. 2.

The rotary electromagnet arrangement of the invention shown in FIG. 3has a generally cylindrical, tubular stator frame 44 of magnetizablematerial from whose inner face four equiangularly spaced integral polepieces 46a 46d project radially. A generally cylindrical rotor 48 ofmagnetizable material is coaxially arranged in the frame 44 and carriesfour integral pole pieces 50a 50d projecting radially outward andsimultaneously alignable with the pole pieces of the frame 44 by angulardisplacement of the rotor 48. The frame 44 carries a non-illustratedcoil for exciting the pole pieces 46a 46d, as will presently becomeapparent.

The rotor 48 is biased toward the illustrated position by anon-illustrated return spring and turns clockwise, as viewed in FIG. 3,through an angle 01 from the position indicated by a broken line F to aposition indicated by a broken line P in which the pole pieces 50a 50dare radially aligned with the pole pieces 46a 46d, whereupon the rotorstops.

When the angle a" is smaller than the complementary angle B, the rotor48 is turned clockwise when the stator is excited. When the angle 01 isgreater than the angle B, the rotor is turned counterclockwise.

When constant current flows through the nonillustrated coil of thestator, the circumferential distance between associated pole pieces ofthe stator and rotor decreases during angular movement of the rotor 48.As indicated by the line a in FIG. 4, the circumferential component ofthe magnetic force exerted on the rotor which causes rotation of therotor has its maximum value in the illustrated rest postiion and becomeszero when the pole pieces of the stator and rotor are aligned in thefinal position.

FIGS. 5(A) to 7(B) and FIG. 10 illustrate an actual embodiment of therotary electromagnet arrangement shown in FIG. 3. Referring initially toFIGS. 5(A) to 5(C), there is seen a stator 52 consisting of twoidentical unitary frame bodies 54 of magnetizable material arrangedsymmetrically relative to the radial plane 5 5 in FIG. 5(A). Each body54 has an outer, circumferential, cylindrical wall portion 56 axiallyengaging the corresponding wall portion of the other body and anannular, radial end wall portion 60 axially remote from the other body54. Six pole pieces 58a 58fare equiangularly distributed about a centralaperture 62 in the end wall portion 60. As is best seen in FIG. 10, thepole pieces are circumferentially spaced fragments of a cylindrical tube64 and axially project from each radial end wall portion 60 towardaxially aligned pole pieces on the other wall portion 60, but areaxially shorter than the wall portions 56. v

The bodies 54 jointly bound an annular cavity S in which a coil 70 isreceived. A rotor 66 is journaled in two bearing plates 72 fitted in theopenings 62. The axial gap d, between the adjacent ends of aligned pairsof pole pieces of the bodies 54 is greater than the radial gap d betweenthe cylindrical surface p defined by the inner circumferential faces ofthe pole pieces 58a 58f and the corresponding opposite surface q of therotor 66. Axially adjacent the gaps 64a 64f which circumferentiallyseparate the pole pieces, the thickness d of the end wall portion 60 ismuch smaller than its thickness d between the pole pieces and thecylindrical wall portion 56. The magnetic fluxfproduced by the energizedcoil 70 thus flows almost entirely in the magnetic circuit indicated inFIG. 5(C) by a broken line from the stator 52 across the gap d into therotor 66 and back through the gap (1, into the stator.

As best seen in FIGS. 7(A) and 7(8), the coil 70 has an excitationwinding 73 on a flanged tube 74 of insulating material. It is fastenedin the cavity S in a conventional manner not specifically illustrated.

The rotor 66 is shown in FIGS. 6(A) and 6(8). It has six axiallyelongated pole pieces 68a to 68fradially projecting from an integral,cylindrical body portion 69 of magnetizable material, and areequiangularly spaced for simultaneous radial alignment with the polepieces of the stator 52. Each pole piece on the rotor is axiallycoextensive with two aligned pole pieces of the stator. The body portion69 is mounted on a shaft 67.

In the modified electromagnet arrangement shown in FIG. 8, the rotor 66is identical with that described above, and the stator has two identicalframe units 78 which differ from those of the afore-described embodimentby pole pieces 80 having obliquely inclined faces 82 which radiallybound the cavity S for the nonillustrated exciting coil. The pole pieces80 thus taper in an axial direction toward each other. This furtherreduces leakage of magnetic fiux between axially aligned pole pieces,provides space for more excitation windings, and facilitates the removalof the units 78 from a mold if they are made by molding.

In the modified rotor 88 shown in FIG. 9, the pole pieces 90 are axiallyelongated and equiangularly distributed about the circumference of therotor body, as described above, but the length W2 of the leading axialedge is smaller than the length w of the trailing axial edge so thateach pole piece tapers circumferentially. As is shown by broken line bin FIG. 4, this modification delays the decrease of the torque exertedon the rotor as it moves from its rest position to a final position ofalignment of the pole pieces on the rotor and stator.

Only preferred embodiment of the electromagnet arrangement of theinvention have been described. Modifications will be apparent to thoseskilled in the art in the light of the above teachings, and it isintended to cover all changes and modifications of the examples of theinvention herein chosen for the purpose of the disclosure which do notdepart from the spirit and scope of the appended claims. What is claimedis: I. A magnet arrangement comprising: a. a casing of magnetizablematerial; b. two annular pole pieces having respective, coaxial, centralopenings, said pole pieces being mounted on said casing in axiallyspaced relationship; c. an annular coil having an excitation windingabout said axis, said coil being axially interposed between said polepieces and having a central opening axially aligned with the openings ofsaid pole pieces; and d. an armature axially slidable in the alignedopenings of said pole pieces and said coil, said armature including 1.two bodies of magnetizable material dimensioned and arranged to bereceived simultaneously in the central openings of said pole pieces whensaid winding is energized, and

2. a rod member axially connecting said bodies, a portion of said rodmember intermediate said bodies consisting of magnetizable material.

2. An arrangement as set forth in claim 1, wherein said casing istubular, said pole pieces being mounted on the inner wall of saidcasing.

3. A magnet arrangement comprising:

a. a stator including 1. An annular frame of magnetizable material, saidframe having an axis, two axially spaced, radially extending end walls,and an outer circumferential wall connecting said end walls, said endwalls being formed with respective central openings,

2. a plurality of pole pieces of magnetizable material circumferentiallyspaced about the central opening of each of said end walls and extendingfrom the associated end wall toward a pole piece on the other end wall,the pole pieces on one end wall being axially spaced from the polepieces on the other end wall, said walls and said pole pieces jointlybounding an annular cavity, and

3. a coil having excitation windings in said cavity;

and

b. a rotor mounted for rotation about said axis, said rotor including 1.a body portion of magnetizable material and 2. a plurality of polepieces of said material radially projecting from said body portion incircumferentially spaced relationship for simultaneous radial alignmentwith the pole pieces on said end walls.

4. An arrangement as set forth in claim 3, wherein said frame consistsessentially of two substantially identical bodies, each body includingone of said end walls and an axial portion of said circumferential wall,the

pole pieces on the end wall of each body being axially 5 aligned withthe pole pieces on the other body and equiangularly spaced about saidaxis.

5. An arrangement as set forth in claim 4, wherein said pole pieces ofsaid rotor are axially coextensive with the pole pieces on both endwalls.

6. An arrangement as set forth in claim 3, wherein the axial spacing ofthe pole pieces on each end wall from the pole pieces on the other endwall is greater than the radial spacing of the pole pieces of said rotorfrom the pole pieces of said stator during said simultaneous radialalignment.

7. An arrangement as set forth in claim 3, wherein the pole pieces onsaid end walls have respective faces opposite said circumferential wall,said faces bounding said cavity and being obliquely inclined relative tosaid axis, and each of the pole pieces on said end walls tapers axiallyaway from the associated end wall.

8. An arrangement as set forth in claim 3, wherein the pole pieces ofsaid rotor are each axially elongated and taper circumferentially.

9. A frame for a magnet arrangement comprising two substantiallyidentical, approximately cup-shaped bodies of magnetizable materialhaving a common axis and being axially juxtaposed in abutting engagementalong a plane of symmetry radial relative to said axis, each bodyincluding a. an outer circumferential wall portion axially engaging thecorresponding wall portion of the other body.

b. a radially extending wall portion axially remote from the other bodyand formed with a central aperture, and

c. a plurality of pole pieces projecting axially from said end walltoward the pole pieces on the end wall of the other body,

1. said pole pieces being circumferentially spaced about said centralaperture,

2. each pole piece being axially aligned with a pole piece on the otherend wall and axially spaced from the axially aligned pole piece.

10. A frame as set forth in claim 9, wherein said pole pieces areequiangularly spaced about the central aperture of the associated endplate.

1. A magnet arrangement comprising: a. a casing of magnetizablematerial; b. two annular pole pieces having respective, coaxial, centralopenings, said pole pieces being mounted on said casing in axiallyspaced relationship; c. an annular coil having an excitation windingabout said axis, said coil being axially interposed between said polepieces and having a central opening axially aligned with the openings ofsaid pole pieces; and d. an armature axially slidable in the alignedopenings of said pole pieces and said coil, said armature including 1.two bodies of magnetizable material dimensioned and arranged to bereceived simultaneously in the central openings of said pole pieces whensaid winding is energized, and
 2. a rod member axially connecting saidbodies, a portion of said rod member intermediate said bodies consistingof magnetizable material.
 2. a rod member axially connecting saidbodies, a portion of said rod member intermediate said bodies consistingof magnetizable material.
 2. An arrangement as set forth in claim 1,wherein said casing is tubular, said pole pieces being mounted on theinner wall of said casing.
 2. a plurality of pole pieces of saidmaterial radially projecting from said body portion in circumferentiallyspaced relationship for simultaneous radial alignment with the polepieces on said end walls.
 2. a plurality of pole pieces of magnetizablematerial circumferentially spaced about the central opening of each ofsaid end walls and extending from the associated end wall toward a polepiece on the other end wall, the pole pieces on one end wall beingaxially spaced from the pole pieces on the other end wall, said wallsand said pole pieces jointly bounding an annular cavity, and
 2. eachpole piece being axially aligned with a pole piece on the other end walland axially spaced from the axially aligned pole piece.
 3. a coil havingexcitation windings in said cavity; and b. a rotor mounted for rotationabout said axis, said rotor including
 3. A magnet arrangementcomprising: a. a stator including
 4. An arrangement as set forth inclaim 3, wherein said frame consists essentially of two substantiallyidentical bodies, each body including one of said end walls and an axialportion of said circumferential wall, the pole pieces on the end wall ofeach body being axially aligned with the pole pieces on the other bodyand equiangularly spaced about said axis.
 5. An arrangement as set forthin claim 4, wherein said pole pieces of said rotor are axiallycoextensive with the pole pieces on both end walls.
 6. An arrangement asset forth in claim 3, wherein the axial spacing of the pole pieces oneach end wall from the pole pieces on the other end wall is greater thanthe radial spacing of the pole pieces of said rotor from the pole piecesof said stator during said simultaneous radial alignment.
 7. Anarrangement as set forth in claim 3, wherein the pole pieces on said endwalls have respective faces opposite said circumferential wall, saidfaces bounding said Cavity and being obliquely inclined relative to saidaxis, and each of the pole pieces on said end walls tapers axially awayfrom the associated end wall.
 8. An arrangement as set forth in claim 3,wherein the pole pieces of said rotor are each axially elongated andtaper circumferentially.
 9. A frame for a magnet arrangement comprisingtwo substantially identical, approximately cup-shaped bodies ofmagnetizable material having a common axis and being axially juxtaposedin abutting engagement along a plane of symmetry radial relative to saidaxis, each body including a. an outer circumferential wall portionaxially engaging the corresponding wall portion of the other body. b. aradially extending wall portion axially remote from the other body andformed with a central aperture, and c. a plurality of pole piecesprojecting axially from said end wall toward the pole pieces on the endwall of the other body,
 10. A frame as set forth in claim 9, whereinsaid pole pieces are equiangularly spaced about the central aperture ofthe associated end plate.